Anthrax scares continued to rattle the nerves of people across the nation—including at Harvard—yesterday.

An e-mail made the rounds of House open lists last night saying that a threat had been directed against the libraries and asking people to stay away last night.

However, Harvard University Police Department (HUPD) Sgt. Kevin P. Bryant said last night that students did not have to worry.

He said the department was aware of a nonspecific threat received yesterday, but that a thorough investigation had uncovered nothing.

Nonetheless, HUPD officers would remain vigilant of any suspicious activity at the libraries, Bryant said.

HUPD has been kept busy with reports of suspicious activities and suspicious mail at the University in recent days, including a minor incident at Eliot House Tuesday night when a student found a piece of mail that he did not recognize.

The mail turned out to be an innocuous invoice.

But despite the lack of any credible threats against any area universities, tensions remained high.

MIT officials announced that tests done on a suspicious piece of mail found there Tuesday had proved negative for anthrax.

According to a MIT press release, officials at the Massachusetts State Laboratory in Jamaica Plain carried out tests yesterday which showed that the powder tested negative for the anthrax bacterium.

MIT authorities contacted the Cambridge Fire Department Hazardous Materials Team on Tuesday when a lecturer in the school’s foreign languages and literature department opened a letter to find about a teaspoon of white powder.

A second scare at MIT on Tuesday was resolved when officials determined that the white powder on another envelope was, in fact, construction dust.

—Staff writer Alex B. Ginsberg can be reached at ginsberg@fas.harvard.edu.

—Staff writer Garrett M. Graff can be reached at ggraff@fas.harvard.edu.